This invention concerns a device to check the presence of threads on spinning machines. To be more exact, the invention is applied properly to ring spinning machines.
The invention can be fitted to any spinning machine and is especially advantageous in the case of wet spinning frames for linen or other analogous fibers or the like.
It is known that on spinning machines it is necessary to provide a detector which senses whether or not the thread is passing through.
In fact, if there is no thread, this means that the spool is not being fed and that the spindle is rotating to no purpose; in other words, time and energy are being wasted without achieving any result.
A device to check the presence of the thread in a spinning machine is always associated with another device which is normally positioned upstream of the drafting zone and which serves to halt the thread, so that the thread is not wound on elements in motion and does not damage them or else so that there is no loss of thread being sent to waste.
Devices to check the presence of the thread are known and are of various types. One type includes a sensor to detect the presence of the thread and, if the thread is lacking, a circuit to actuate a thread-arresting device is actuated. Such a type of sensor may be mechanical with a lever or be piezoelectric, or may include a photosensitive element or may operate by Hall effect or with an encoder-type position transducer, etc.
However, these types of sensor are not advantageous in given types of processing on spinning machines, nor are they advantageous with certain types of yarn.
To obviate the drawbacks of these types of sensors, a sensor has been proposed in EP-A-0329618 and is fitted to the ring rail and detects the regular passage of the metallic thread-guide traveller.
This metallic thread-guide traveller in passing in front of the sensor modifies periodically the magnetic field which affects the sensor. By measuring and processing these periodic modifications, a signal indicating the presence or otherwise of the thread is obtained.
This device, which is very accurate and reliable in itself, is no longer accurate when the thread-guide traveller is made of plastic or, at any rate, of a material which has no effect on the sensible magnetic field that affects the sensor.
In this case, where the yarn to be processed requires a thread-guide traveller made of a non-magnetic material, it is necessary to forgo these sensors fitted to the ring rail and to employ sensors that act in direct cooperation with the thread.
As we said earlier, these sensors are less accurate and reliable and also require continuous maintenance work to keep them at a reliable quality level. In fact, the presence of dirt mixed with water lessens the reliability of these sensors considerably.
Document WO-A-88/08047 discloses a sensor which is intended to check the unit length weight or linear density of a sliver being processed. The signal arriving from the sensor positioned in a trumpet has the purpose of regulating the speed of the drawing rolls so as to obtain the greatest possible uniformity of the sliver. The sensor disclosed in this document monitors the acoustic emissions caused by natural compression of the fibers against each other and by their contact with the trumpet through which they are compelled to pass. Therefore, the field of employment of the sensor and its functional nature are clearly different from those for which the sensor of our invention is used.
Document FR-A-2.161.471 discloses a system to monitor the presence of the thread on the basis of the fact that the thread modifies an acoustic signal coming from an emitter of ultrasonic sounds. This system is different from our invention under examination owing to the fact that the acoustic source is produced not in a natural manner by the thread and/or the traveller rotating on the ring of the spinning machine but artificially by an emitter of ultrasonic sounds, and also because the system consists of two active components, namely an emitter and a receiver, and also owing to the fact that this system monitors directly the presence of the thread and works in the field of ultrasonic sounds. All these differences together make the teaching of FR-A-2.161.471 not capable of being applied to the problems which our invention purposes to overcome.
The present applicant has therefore tackled this problem in seeking a solution which meets requirements satifactorily.